The long range goal of this proposal is to understand the macromolecular mechanisms which contribute to the growth of the axon during development and regeneration. This proposal focuses on the cytoskeleton of the axon and its involvement in axonal growth. One objective is to study axonal transport of identified structural proteins in growing axons. Examples of such proteins are tubulin, the subunit protein of microtubules, and actin. These proteins appear to be transported in the slow component of axonal transport. Tubulin will be identified immunochemically with a specific antisera and actin by DNase I affinity chromatography. In these experiments the proteins transported into the axon are labeled with amino acid precursors which are injected directly into the nervous system. The labeled proteins of interest can be analyzed as they are transported along the axon. In order to study the behavior of these proteins during axonal growth. The transport characteristics of these proteins will be analyzed in regenerating axons and compared with normal, intact axons. Another objective of this proposal is to identify proteins which are transported with tubulin in the axon and which may be involved in the regulation of microtubule polymerization and transport. We will look for proteins which are transported in association with tubulin and whose kinetics are altered similarly to those of tubulin in regenerating axons. In order to determine whether these proteins are physically associated with microtubules, the labeled proteins which are transported in the axon will be subjected to an "in vitro" polymerization assay for microtubules. The remaining objective of this proposal is to test our hypothesis that the cessation of axonal growth involves the disassembly of the axonal cytoskeleton at the axon terminal. We propose to determine whether the cytoskeleton is degraded in mature axons after it is transported in the axon to the axon terminal. Collectively, these studies should help us understand how the axonal cytoskeleton contributes to the growth of the axon. Another benefit is the results could be important in shaping our conception of the cellular mechanisms which are involved in stopping axonal growth when the axon reaches an appropriate target cell.